In the case of encoded audio data recorded on a recording medium such as a hard disk, it is possible during special playback to reproduce and output the audio data at a tempo differing from the original one during normal playback. For example, if the viewer cannot clearly understand what is done/spoken in a TV program where persons spoke quickly or in a foreign language, the slow playback capability allows the viewer to view and listen to the program more slowly by lowering the tempo of playing back the program.
To realize a desired speed, however, it is inevitable for the sound quality to deteriorate since the original data must be processed. Thus, it is necessary to work out the control method capable of improving the sound quality. For example, JP2002-278597 discloses a technique for improving the quality of sound output at double speed playback.